1. Field of the Invention
The invention relates to a microfilm viewer/printer, and more particularly to a full plane exposure image projection system for a plain paper microfilm viewer/printer.
2. Discussion of the Prior Art
Microfilm is a well-known medium for storing and/or distributing large volumes of documents. Microfilm viewers are necessary for a user to read the documents stored on microfilm and microfilm printers are necessary to make a paper copy of a document stored on the microfilm. Consequently, machines performing both functions, commonly referred to as microfilm viewer/printers, are commercially available and widespread.
In microfilm viewer/printers, it has typically been the case that in a view mode of the machine, the machine user could observe an image of the document recorded on the microfilm at a viewing screen. In a print mode, the projection system inside the viewer/printer directs the image to a xerographic copying engine inside the viewer/printer which makes a paper copy of the image, typically by a scanning process.
In the scanning process, the image of the document is projected to the copying engine in sections by scanning consecutive portions of the document being reproduced. The scanning speed in such a device must be synchronized with the rate at which a receptor surface of the copying engine is moving. The mechanism for performing the scanning operation adds a level of complexity not necessary in full plane exposure systems. Also, the overall size of the microfilm viewer/printer is larger in order to house the scanning mechanism.
A major difference between microfilm viewer/printers and copy machines is that the object being copied on a copy machine is usually copied at a ratio of no more than 2 to 1 as compared with copies made from microfilm that are copied at a ratio of from about 12:1 up to about 72:1. This difference makes scanning an object on a copy machine relatively non critical whereas the scanning of an object on a microfilm viewer/printer requires extremely smooth movement of the scanning device. Otherwise, the image being scanned will be blurred. The critical nature of the scanning mechanism on a microfilm viewer/printer results in this mechanism being more complex and more costly than the scanning mechanism of a copy machine.
It has become accepted in the industry to provide a carrier for the microfilm which can be moved to position the image of the desired document of the microfilm on the viewing screen. It has also become generally preferred to use a plain paper copying engine, rather than a treated paper type engine. With the plain paper engine, separate sheets of ordinary paper, usually of a standard size, for example 8.5 .times. 11 inch letter size, are placed in a stack in a paper cassette. The copying engine feeds sheets from the cassette as required to make copies and when the copies are made, the engine issues them to the exterior of the machine.
Microfilm viewer/printers utilizing full plane exposure are known, but a major problem with such prior viewer/ printers has been their size, which in large part has been required by their projection systems. Since the viewer/ printers are typically kept on a desk or countertop, it is important that their "footprint" on the countertop be as small as possible. The cost of such machines has also in part been determined by the complexities of the projection systems and the mechanisms associated with the projection systems.